DESCRIPTION: The specific aims of this project are to localize and identify a gene responsible for the perception of the bitter taste of 6-n-propylthiouraci (PROP) and related compounds. This is to be done by screening the PROP perception of a large population which has been ascertained and is being genotyped for a separate study of obesity genes. Sib pair analysis of informative sibships will be used to localize a gene, and particularly discordant pairs will be further tested to refine the phenotype and perform additional linkage analysis. Haplotyping and association analysis will be use to further narrow the interval likely to contain the gene. The function of genes localized to the region will be examined to determine if they are likely candidates, with particular attention to genes involved in transduction in retinal cells, since there is evidence of homology with the mechanisms of tast receptors. Known variations in such genes will be tested for co-segregation with the PROP phenotype. If there are no known candidate genes, expressed sequences will be similarly evaluated.